1. Technical Field
This application generally relates to sample introduction, and more particularly to techniques used in connection with sample injection apparatus and techniques.
2. Description of Related Art
Samples may be processed in a laboratory or other environment for a variety of different purposes and applications. Chromatography refers to techniques for separating sample mixtures. Common chromatographic techniques include gas chromatography (GC) and liquid chromatography (LC). With an instrument that performs LC, a liquid sample to be analyzed is introduced in small volumes for analysis. The sample may be injected into a solvent stream which is carried through a column. The compounds in the sample can then be separated by traveling at different speeds through the column resulting in the different compounds eluting from the column at different times. In connection with High Performance Liquid Chromatography (HPLC) and Ultra Performance Liquid Chromatography (UPLC), pressure is used to facilitate fluid flow in the system through the chromatographic column.
In a system that performs LC, a sample may be injected into the system using different techniques. One technique is fixed loop injection where a sample may be aspirated into a needle, positioned in a sample loop, and then carried through to the column. With fixed loop injection, the sample loop becomes part of the fluid path. Another technique is direct injection where a sample is aspirated into a needle and the sample is directly injected into the system so that the needle becomes part of the fluid path. With direct injection, after the sample is aspirated into a needle, the needle may be positioned at a surface of a sealing member. The needle has sufficient force applied thereto so that the needle tip forms a seal at the surface of the sealing member when the LC system is subsequently pressurized. The sample in the needle is then carried through to the column, such as by a solvent. The needle used with direct injection may be subject to buckling due to the amount of force applied in connection with forming the seal. Additionally, needle washing is part of the processing typically performed in connection with direct injection techniques. After the sample is injected and after completion of the associated chromatographic run for the sample, the needle may be subject to a wash sequence where the outside of the needle is washed with a solvent, solution, or the like, to remove any remaining sample from the needle.